Dandy-Walker malformation

Dandy-Walker malformation (DWM) is the most common posterior fossa malformation, characterized by the triad of:

  • hypoplasia of the vermis and cephalad rotation of the vermian remnant
  • cystic dilatation of the fourth ventricle extending posteriorly 
  • enlarged posterior fossa with torcular-lambdoid inversion (the torcula lying above the level of the lambdoid due to abnormally high tentorium)

Terminology

This article focuses on the "classic" presentation of Dandy-Walker malformation, please refer to Dandy-Walker continuum for a discussion on other related posterior fossa malformations.

The term “classic Dandy-Walker malformation” and others like “Dandy-Walker variant” or “Dandy-Walker complex”, were created to differentiate those malformations that do not meet the criteria for Dandy-Walker malformation, however, some authors recommend to avoid them as they have a lack of specificity that may create some confusion. Instead, a more detailed anatomic description is recommended .

Epidemiology 

The estimated prevalence of a Dandy-Walker malformation and related variants is about 1 per 30,000 live births and accounts for ~7.5% (range 4-12%) of the cases of infantile hydrocephalus. It is known as the most common posterior fossa malformation .

Clinical presentation

Clinical presentation is dependent on the severity of the abnormality. In a classic Dandy-Walker malformation, patients usually manifest in the first year of life with symptoms of hydrocephalus and associated neurological symptoms. Macrocephaly is the most common manifestation and in ~80% of cases, the diagnosis is made by the first year of life. Despite severe cerebellar abnormalities, cerebellar signs are not common.

Pathology

Many have a sporadic inheritance with some possibly having an autosomal dominant or X-linked inheritance.

Associations

Radiographic features

Ultrasound

Antenatal sonographic features that would suggest the diagnosis include the combination of :

Antenatal ultrasound may falsely overdiagnose the condition if performed before 18 weeks, as the vermis has not properly formed.

MRI

MRI is the modality of choice for assessment of Dandy-Walker malformation, although both CT and ultrasound will demonstrate the pertinent features.

Classically Dandy-Walker malformation consists of the triad of:

  • hypoplasia of the vermis and cephalad rotation of the vermian remnant
  • cystic dilatation of the fourth ventricle extending posteriorly; usually the cerebellar hemispheres are displaced anterolaterally, but with a normal size and morphology
  • enlarged posterior fossa with torcular-lambdoid inversion (torcular lying above the level of the lambdoid due to abnormally high tentorium)

In 75-90% of patients, obstructive hydrocephalus is evident by three months of age , in many cases due to aqueduct stenosis . CSF flow study is recommended to better assess the hydrodynamic changes and identify eventual aqueductal stenosis association, which cannot be treated by cystoperitoneal shunt placement .

Treatment and prognosis

A Dandy-Walker malformation carries a high mortality rate, ~70% in live-born fetuses, often due to associated abnormalities . It is thought to carry a poorer prognosis if diagnosed prior to 21 weeks of gestation and a better prognosis if diagnosed postnatally . A cystoperitoneal shunt could be considered in situations where hydrocephalus is significant problem. Even in the absence of any associated syndromes, there is a recurrence risk of ~2.5% (range 1-5%) in subsequent pregnancies.

History and etymology

It was initially described by Blackman and Dandy in 1914 .

Differential diagnosis

The differential is that of other causes of an enlarged CSF retrocerebellar space (and mimics thereof) including:

On antenatal ultrasound, also consider technical and timing factors such as:

  • too steep insonation angle
  • a scan performed too early in gestation, i.e. prior to 18 weeks